nfp: don't reuse pointers in ring dumping

We were reusing skb pointer when reading page frag, since ring
entries contain a union of a skb and frag pointer.  This can
be confusing to people reading the code.  Refactor the code
to read frag pointer directly.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Jakub Kicinski

drivers/net/ethernet/netronome/nfp/nfp_net_debugfs.c

@@ -125,7 +125,6 @@ static int nfp_net_debugfs_tx_q_read(struct seq_file *file, void *data)
 	struct nfp_net_tx_ring *tx_ring;
 	struct nfp_net_tx_desc *txd;
 	int d_rd_p, d_wr_p, txd_cnt;
-	struct sk_buff *skb;
 	struct nfp_net *nn;
 	int i;
 
@@ -158,13 +157,15 @@ static int nfp_net_debugfs_tx_q_read(struct seq_file *file, void *data)
 			   txd->vals[0], txd->vals[1],
 			   txd->vals[2], txd->vals[3]);
 
-		skb = READ_ONCE(tx_ring->txbufs[i].skb);
-		if (skb) {
-			if (tx_ring == r_vec->tx_ring)
+		if (tx_ring == r_vec->tx_ring) {
+			struct sk_buff *skb = READ_ONCE(tx_ring->txbufs[i].skb);
+
+			if (skb)
 				seq_printf(file, " skb->head=%p skb->data=%p",
 					   skb->head, skb->data);
-			else
-				seq_printf(file, " frag=%p", skb);
+		} else {
+			seq_printf(file, " frag=%p",
+				   READ_ONCE(tx_ring->txbufs[i].frag));
 		}
 
 		if (tx_ring->txbufs[i].dma_addr)